Production of nitriles



United States Patent PRODUCTION OF NITRILES Harry B. Copelin, NiagaraFalls, N. Y., assignor to E. I. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware N0 Drawing. ApplicationNovember 19, 1952, Serial No. 321,510

22 Claims. (Cl. 260--465.8)

This application relates to the production of nitriles and moreparticularly to the reaction between a metal cyanide and an organichalide to produce a nitrile. it is a continuation-in-part of applicationSerial No. 251,140, filed October 12, 1951, now abandoned.

Heretofore nitriles have been produced by reacting organic halides withmetal cyanide in non-aqueous media. In such reactions the best resultsgenerally have been obtained by selecting as the medium or solvent forthe reaction an organic liquid which has considerable solvent power forthe metal halide. For example, in producing nitriles by reacting organichalides with an alkali metal cyanide such as sodium cyanide, thepreferred reaction solvents have been alcohols or ether-alcohols,liquids which dissolve the organic halides and also the alkali metalcyanide to a considerable extent. Such solvent media for thenitrile-forming reaction are disclosed for example in Macallurn U. S. P.2,211,240 and Rogers U. S. P. 2,415,261.

The above-mentioned Rogers patent discloses, among other things, theproduction of adiponitrile by reaction of 1,4-dichlorobutane with sodiumcyanide in an etheralcohol as reaction medium. This process forproducing adiponitrile results in yields which are good but neverthelesslimited by the by-product tars and ethers formed.

An object of this invention is, therefore, to provide an improved methodfor the production of a nitrile by the reaction of an organic halidewith a metal cyanide.

A further object is to provide an improved liquid medium for carryingout such reaction. A still further object is to provide an improvedprocess for the production of adiponitrile and other saturated aliphaticdinitriles by the reaction of an alkali metal cyanide with thecorresponding saturated aliphatic dihalides or saturated aliphaticcyanohalides. Still other objects will be apparent from the descriptionof the invention.

The above-stated objects may be attained in accordance with the presentinvention by reacting a metal cyanide with an aliphatic organic compoundcontaining at least one halogen atom of atomic weight not less than 35and having not more than two of such halogen atoms linked to a singlecarbon atom, at least one of said halogen atoms being linked to anon-tertiary carbon atom, in a liquid reaction medium initiallycontaining not less than about and preferably 40%, by weight of adialkyl amide of a fatty acid. The dialkyl amide, which serves asreaction solvent, has an eflect on the course of the reaction,increasing the yield of nitrile and decreasing the amount of non-nitrilelay-products. Suitable solvents are the N-dialkyl amides of formic,acetic and propionic acids which have not more than two carbon atoms ineach N-alkyl radical.

The invention is illustrated by the following examples:

Example 1 Chlorotrimethyl acetonitrile, 356 g., sodium cyanide, 160 g.,sodium iodide, 16 g., and methyl Cellosolve (monomethyl ether ofethylene glycol), 300 cc., were ice charged to a one-liter steel bomband heated at 200220 C. for 12 hours. The bomb was cooled, emptied, andthe product filtered to remove inorganic salts. Distillation of thefiltrate yielded 40 g. (12%) of very crude dinitrile boiling at ll0130C. at 25 mm.

Example 2 Chlorotrimethyl acetonitrile, 117 g., was added over a 2-hourperiod to a refluxing mixture of sodium cyanide, 50 g., and dimethylacetamide, 300 g. After the addition was complete the reaction mixturewas refluxed for 2 hours, then cooled and filtered. Distillation of thefiltrate at 25 mm. yielded 68 g. (62%) of good quality dinitrile boilingpractically all at C. at 25 mm.

Example 3 1,4-dichloro n-pentane, 500 g., was added to a refluxingmixture of methyl Cellosolve, 1000 cc., and sodium cyanide, 400 g., asrapidly as possible. The reaction mixturewas then refluxed for 2 hours.At the end of this time the product was filtered, the cake Washed oncewith methyl Cellosolve, and the filtrate distilled under reducedpressure. There was recovered 332 g. (72%) of delta-chlorocapronitrileand 87 g. (b. 140 C. at 5 mm.) (20%) of alpha methyl adiponitrile.

Example 4 1,4-dichloro n-pentane, 141 g., was added to a refluxingmixture of sodium cyanide, 120 g., and dimethyl formamide, 350 cc., overa one hour period. Refluxing was continued for 2 hours, then the mixturewas cooled, filtered, and the cake washed once with methylene chloride.Distillation of the filtrate at 10 mm. pressure yielded 3 g. ofchloronitrile (2%) and 102 g. (83%) of alpha methyl adiponitrile,boiling -1 60 C. at 10 mm.

Example 5 'y-Chlorovaleronitrile, 100 g., was added over a /2-hourperiod to a mixture of 50 g. of sodium cyanide in 300 cc. of dimethylformamide at reflux temperature. After the addition, the reactionmixture was refluxed for one hour, cooled, and filtered. The cake wassucked dry and the filtrate distilled under reduced pressure. 78 g.(85%) of alpha methyl glutaronitrile (b. 140-145 C. at 20 mm.) wasobtained.

Example 6 Methyl Cellosolve, 2070 g., and 96% sodium cyanide, 1085 g.,were mixed and heated to reflux. 1,4-dichlorobutane, 1350 g., was run inwith stirring over a 2-hour period, then reflux was continued for 100minutes. The reaction mixture was cooled, filtered, and the filter cakeexhaustively washed with methylene chloride. Vacuum distillation of thefiltrate produced 25 g. (2%) of deltachlorovaleronitrile and 1022 g.(89%) of adiponitrile. Also produced was about 100 g. of tars andby-products boiling between chlorovaleronitnle and adiponitrile.

Example 7 Dimethyl formamide containing 1% water, 2070 g., and 96%sodium cyanide, 1085 g., were heated to reflux under mm. pressure (100C.). Dichlorobutane (1350 g.) was run in with stirring over a one hourperiod, then reflux was continued for 120 minutes. The reaction mixturewas cooled, filtered, and the filter cake washed thoroughly withmethylene chloride. Vacuum distillation of the filtrate produced 52 g.(4.1%) of delta-chlorovaleronitrile and 1063 g. (93.5%) of adiponitrile.The tars and other by-productsformed amounted to only 25 g., a 75%reduction as compared with the previous example.

Example 8 2-chlorobutane, g., was added to a refluxing mix- Example 92-chlorobutane, 185 g., was added to a refluxing mixture of sodiumcyanide, 105 g. (98%), and methyl Cello.-

solve, 500 cc., over a period of two hours. Refluxing was continued fortwo hours, then the mixture was cooled, filtered, and thesalt cakewashed with methylene chloride. Titration of the salt cake for chlorideion showed that 6.7% of the organic chloride was converted to inorganicchloride. Distillation of the filtrate yielded only the startingmaterial, 2:chlorobutane,.

Example 10 p A series of runs was made by charging sodium cyanideand'dichlorobutane into dimethylformarnide to determine the lowestconcentration of the latter capable of effective performance. Each runwas prolonged for two hours. Reference reactions in a mixture containingabout 40% by weight of solvent dimethyl formamide show 90-95% conversionof the dichlorobutane to chlorovaleronitrile and adiponitrile in such aperiod. When the weight of the. solvent was. reduced to 20% of the totaland the temperature of the mixture held at 120150 C. for two hours, aconversion of only 60% was obtained. At a temperature of. l20l50 C. amixture containing 300 g. of dichlorobutane, 200 g. of sodium cyanideand by Weight of solvent showed a conversion of only 30%, the productconsisting of 42 g. of chlorovaleronitrile and 27 g; of adiponitrile. Inthis case no reaction at all was evident after an initial rather violentupsurge in temperature had been checked. Another run made with a solventcomprising only 5% of the mixture but at a temperature. of 100 C. gavea. quiet steady reaction with a 40% conversion in the allocated twohours. A final run made. at 21/2%. dimethylformamide concentration byweight and at l20-l50 C. gave no further reaction after an introductoryspurt with an apparent conversion even smaller than that obtained with5% solvent. From these experiments it is evident that, in thedichlorobutane cyanation at least, a concentration of dimethylformamidesolvent of at least 40% is preferred. A solvent concentration of- 20-40%can be utilized but requires more time to achieve a given'conversionthan does a higher proportion of diluent. Concentrations below about 20%result in impracticably slow reactions and, in addition, seem to favorthe replacement of one rather than of two halide ions.

The liquid reaction solvents or reaction media employed in the presentinvention are the N-dialkyl amides of formic, acetic and propionic acidshaving not more than two carbon atoms ineach N-alkyl radical. Thesedialkyl amides may be represented by the type formula RCONXz wherein R-represents hydrogen and alkyl radicals having not more than two carbonatoms and X represents alkyl radicals having not more than twocarbonatoms. Examples of the N-dialkyl amides are: dimethyl formamide,dimethyl acetamide, diethyl formamide, diethyl acetan'ride, methyl ethylformamide, methyl ethyl acetamide, dimethyl propionamide, diethylpropionamide and methyl ethyl propionamide.

The extent to which the benefits of this invention are obtained dependsupon the amount of the dialkyl amide present in the reaction mixture.Good results generally may be obtained when the liquid portion of thereaction mixture initially contains from,40 to 95% by weight or more ofthe dialkyl amide. Concentrations of as low as 20% may be employed iflengthened reaction times are tolerable. Solvent concentration below 20%tends to yield erratic reactions and are not desirable. The initialdialkyl amide concentration may be practically 100%; i. e., the halogencompound may be added to a suspension of cyanide in the dialkyl amide orthe two reactants may be simultaneously added to the dialkyl amide. Thepreferred initial concentration of the dialkyl amide, at which bestresults usually are obtained, is from about to: by weight, or more.Preferably, the dialkyl amide concentration in the liquid portion ismaintained at not less than about 20 to 60%, the 4060% range beingpreferred throughout the reaction. Either a single dialkyl amide or amixture of two or more of the dialkyl amides may be utilized, asdesired.

While the reaction generally is carried out in the anhydrous condition,small amounts of water generally are beneficial. The best results areobtained by adding from a fraction of 1% up to around 2% by weight ofwater to the reaction mixture, either before or during the reaction. v

While the optimum reaction temperature will vary depending upon theparticular organic halide and cyanide reacted, in general the reactionwill occur with a satisfactory yield of nitrile within the temperaturerange of about 20 to 200 C. Generally a reaction temperature of fromabout to C. is preferred. In most cases the best results are obtained bycarrying out the reaction at the atmospheric boiling point of thereaction mixture, i. e.,. at reflux temperature at atmospheric pressure.In cases where the optimum or desired reaction temperature is above theatmospheric boiling point of the chlorohydrocarbon or of the dialkylamide used as liquid reaction medium, the reaction may be carried outunder superatmospheric pressure suflicient to maintain the components ofthe reaction mixture in the liquid state. Subatmospheric pressures maybe employed, to operate at reflux when the desired reaction temperatureis below the atmospheric boiling point of the reaction mixture.

Organic halogen compounds which may be utilized to practice my inventionare aliphatic compounds (including those containing cycloaliphaticgroups) having one or. more halogen atoms of the kind noted below,provided that such halogen atoms are linked to non-tertiary (i. e.,primary or secondary) carbon atoms and also provided that not more thantwo of such halogen atoms are linked to the same carbon atom. I preferto employ chloro compounds which contain no other halogen.

The organic halogen compound may contain functional groups such ascyano, carboxyl, carboxylate (ester or salt), ether, hydroxyl, keto,aldehydo radicals and the like. Compounds containing carboxyl radicals,which tend to react with alkali metal cyanides, preferably are convertedto esters or salts before reacting withvthe cyanide. Generally the bestresults are obtained when the organic compound is a halohydrocarbon or ahalonitrile.

Suitable organic halogen compounds include halogenated polymericmaterials, for example, polyvinyl chloride and polychloroprene, whichmay be reacted in accordance with my invention to produce polymerscontaining cyano groups.

While the examples show the reaction 'ofcyanide with organic chlorides,preferred for reasons of economy, the invention is likewise applicableto the reaction of cyanides with the corresponding bromides and iodides.That is, the reactive halogen atom or atoms are those of atomic weightnot lower than 35. The presence of fluoride (a halogen atom of atomicweight below 35) in the organic compound will not prevent the cyanationreaction if the compound also contains chlorine, bromine or iodine, butthe fluorine atom exhibits little or no reactivity. Accordingly, whilemy invention is retIicted to organic compounds of chlorine, bromine oriodine, I do not exclude suchcompounds which also contain fluorine.

The reaction ofa cyanide with an organic dihalide carried out inaccordance with the present invention, for example, the reaction ofdichlorobutane to produce adiponitrile, generally occurs in two stages,the first producing the chloronitrile and the second converting thechloronitrile to the dinitrile. Accordingly, the invention may beutilized for reacting a metal cyanide with a chloronitrile to produce apolynitrile.

The known nitrile-forming cyanides, i. e., the metal cyanides generallyuseful for reacting with organic halogen compounds to produce nitriles,may be utilized in the practice of this invention. These include thealkali metal cyanides, e. g., sodium cyanide and potassium cyanide, orheavy metal cyanides, e. g., cuprous cyanide or zinc cyanide.

Although dimethyl formamide is a poorer solvent for sodium cyanide thanis the monomethyl ether of ethylene glycol, employment of the former asreaction medium to react 1,4-dichlorobutane with cyanide results in adistinctly larger yield of adiponitrile and a smaller amount of tarryproducts and by-product ethers. In addition to the improved yield anddecreased by-product in the reaction to produce adiponitrile, thepresent invention is useful for making many nitriles which are notobtained at all or are obtained only in very poor yield in reactionsutilizing conventional solvent media.

I claim:

1. A process for the production of a nitrile which comprises reacting anitrile forming metal cyanide with an aliphatic organic compoundcontaining at least one halogen atom of atomic weight not less than 35,and having not more than two of said halogen atoms on a single carbonatom, at least one of said halogen atoms being linked to a non-tertiarycarbon atom, in a liquid reaction mixture initially containing not lessthan about 40% by weight of at least one amide selected from the groupconsisting of the N-dialkyl amides of formic, acetic and propionic acidswhich contain not more than two carbon atoms in each N-alkyl radical.

2. The process according to claim 1 in which said metal cyanide is analkali metal cyanide.

3. The process according to claim 2 in which said amide is a dialkylformamide having not more than two carbon atoms in each N-alkyl radicaland the reaction temperature is within the range of about 20 to 200 C.

4. The process according to claim 2 in which said amide is dimethylformamide and the reaction temperature is within the range of about 20to 200 C.

5. The process according to claim 2 in which said amide is a dialkylacetamide having not more than two carbon atoms in each N-alkyl radicaland the reaction temperature is within the range of about 20 to 200 C.

6. The process according to claim 2 in which said amide is dimethylacetamide and the reaction temperature is within the range of about 20to 200 C.

7. A process for the production of a dinitrile which comprises reactingan alkali metal cyanide with an aliphatic dichloride having chlorineatoms on separate nontertiary carbon atoms in a liquid reaction mixtureinitially containing not less than about 40% by weight of at least oneamide selected from the group consisting of the N-dialkyl amides offormic, acetic and propionic acids which contain not more than twocarbon atoms in each N-alkyl radical, at a temperature of about 20 to200 C.

8. The process according to claim 7 in which said amide is dimethylformamide.

9. The process for the production of a nitrile which comprises reactingan alkali metal cyanide with 1,4-dichlorobutane at a temperature ofabout 100 to 175 C. in a liquid reaction mixture initially containingnot less than about 60% by weight of an amide selected from the groupconsisting of the N-dialkyl amides of formic, acetic and propionic acidswhich contain not more than two carbon atoms in each N-alkyl group.

10. The process for the production of a nitrile which comprises reactingan alkali metal cyanide with 1,4-

dichlorobutane at a temperature of about to C. in a liquid reactionmixture initially containing not less than about 60% by weight of anN-dialkyl formamide having not more than two carbon atoms in eachN-alkyl radical.

11. The process for the production of a nitrile which comprises reactingan alkali metal cyanide with 1,4- dichlorobutane at a temperature ofabout 100 to 175 C. in a liquid reaction mixture initially containingnot less than about 60% by weight of dimethyl formamide.

12. The process for the production of a nitrile which comprises reactingan alkali metal cyanide with 1,4- dichlorobutane at a temperature ofabout 100 to 175 C. in a liquid reaction mixture initially containingnot less than about 60% by weight of dimethyl acetamide.

13. The process for the production of a nitrile which comprises reactingan alkali metal cyanide with an aliphatic halonitrile wherein eachhalogen atom reactive with the cyanide has an atomic weight not lessthan 35 and is linked to a non-tertiary carbon atom, said nitrile havingnot more than two of said halogen atoms linked to a single carbon atomat a temperature of about 100 to 175 C. in a liquid reaction mixtureinitially containing not less than about 60% by weight of an amideselected from the group consisting of the N-dialkyl amides of formic,acetic and propionic acids which contain not more than two carbon atomsin each N-alkyl group.

14. The process of claim 13, wherein said halonitrile is amonochloronitrile and said amide is an N-dialkyl formamide having notmore than two carbon atoms in each N-alkyl radical.

15. The process of claim 13, wherein said halonitrile isdelta-chlorovaleronitrile and said amide is dimethyl formamide.

16. The process according to claim 7 in which said dichloride is analpha-omega dichloride of a saturated aliphatic hydrocarbon and saidamide is an N-dialkyl formamide having not more than two carbon atoms ineach N-alkyl group.

17. The process for the production of a nitrile which comprises reactingan alkali metal cyanide with 1,4- dichlorobutane at a temperature ofabout 100-175 C. in a liquid reaction mixture containing not less thanabout 20% by weight of an N-dialkyl amide having not more than twocarbon atoms in each N-alkyl radical.

18. The process of claim 17 in which the amide is dimethyl formamide.

19. The process of claim 17 in which the amide is dimethyl acetamide.

20. A process for the production of adiponitrile which comprisesreacting 1,4-dichlorobutane with a metallic cyanide in a liquid reactionmedium comprising dimethylformamide.

21. The method of producing adiponitrile by replacing both chlorineatoms in 1,4-dichlorobutane with nitrile radicals which comprisesreacting said dichlorobutane with a metal cyanide in dimethylformamideat a temperature of between about 100 C. and 175 C.

22. The method of producing adiponitrile by replacing both chlorineatoms in 1,4-dichlorobutane with nitrile radicals which comprisesreacting said dichlorobutane with a metal cyanide in a reaction mixturecontaining between about 20% and 60% of dimethylformamide by weight andat a temperature of between about 100 C. and 175 C.

References Cited in the file of this patent UNITED STATES PATENTS2,211,240 Macallum Aug. 13, 1940 2,415,261 Rogers Feb. 4, 1947 2,462,388Hager Feb. 22, 1949 FOREIGN PATENTS 333,989 Great Britain Aug. 28, 1930

1. A PROCESS FOR THE PRODUCTION OF A NITRILE WHICH COMPRISES REACTING ANITRILE FORMING METAL CYANIDE WITH AN ALIPHATIC ORGANIC COMPOUNDCONTAINING AT LEAST ONE HALOGEN ATOM OF ATOMIC WEIGHT NOT LESS THAN 35,AND HAVING NOT MORE THAN TWO OF SAID HALOGEN ATOMS ON A SINGLE CARBONATOM, AT LEAST ONE OF SAID HALOGEN ATOMS BEING LINKED TO A NON-TERTIARYCARBON ATOM, IN A LIQUID REACTION MIXTURE INITIALLY CONTAINING NOT LESSTHAN ABOUT 40% BY WEIGHT OF AT LEAST ONE AMIDE SELECTED FROM THE GROUPCONSISTING OF THE N-DIALKYL AMIDES OF FORMIC, ACETIC AND PROPIONIC ACIDSWHICH CONTAIN NOT MORE THAN TWO CARBON ATOMS IN EACH N-ALKYL RADICAL.